Terminal wall mounted electrical box assemblies for switches and power outlets which are customarily equipped with face plates are prone to misaligned wall mounting problems. Proper electrical box assembly mounting requires that the covering face plate rests flushly against the exterior surface of the abutting wall. Frequently too much or too little of the wall box cut-out space is left exposed after the installation which makes it particularly difficult to flushly match the wall box and the wall cut-out section surface with the electrical box covering face plate. Frequently the cut-out wall section or wall mount positioning of the box is so misaligned that it is impossible to mount the face plate flushly against the exterior wall surface. Moreover it is most difficult under existing technology to seat the terminal electrical units (e.g. switching, power outlets, etc.) onto its wall box mounts so as to provide a face plate mounting which flushly nests against the exposed sections of the terminal electrical unit and the wall surface surrounding the wall mounted terminal electrical box assembly. This results in a tedious task of consistently repositioning the housing terminal electrical connectors (such as switches or power plug-in source connections) at the appropriate depth and placement so as to permit a flush face plate alignment with the covered receptacle as well as being in corresponding alignment with the cut-out portion and the surfacing face of the abutting wall. This perplexing problem can be effectively solved by providing a unique spacing member of a sufficient length, size and compressibility which when properly secured to an electrical box assembly allows a terminal electrical activating power source unit and a face plate to be placed in perfect alignment and interfacial contact with the abutting wall surface. This is achieved with nominal installation effort. The compressible spacing member allows the installer to monitor and control the mounting depth of the terminal electrical unit within the electrical box as well as its mounting interrelationship to the abutting wall surface so as to allow for a perfected flush face plate mounting thereto.